1. Field of the Invention
The present invention relates to an apparatus for measuring static friction force and, in particular, to an apparatus for measuring the static friction force between a magnetic disk and a magnetic head of a hard disk unit.
2. Description of the Related Art
In recent years, the requirement for increasing the storage capacity of the hard disk units has made it necessary to increase the density of magnetic disks. The current trend, therefore, is toward decreasing the flying height of the magnetic head above the magnetic disk. Specifically, in the case where an increased recording density of a magnetic disk is desired for the hard disk unit, the magnetic disk and the magnetic head are required to operate in positions closer to each other by reducing the spacing therebetween. For a stable air-bearing characteristic of the magnetic head to be maintained with a decreased flying height of the magnetic head from the magnetic disk, a smooth surface of the magnetic disk is required. Once the surface of the magnetic disk is smooth, however, the magnetic disk in a stationary state and the magnetic head attract each other. This poses the problem of a larger torque required for restarting the hard disk unit.
In order to obviate this problem, vigorous tribology research and development efforts are continuing to solve the two conflicting objects of smoothing the surface of the magnetic disk on the one hand and preventing the attraction of the magnetic head to the surface of the magnetic disk in stationary state on the other. The demand is very high, therefore, for an apparatus capable of measuring the static friction force between the magnetic head and the magnetic disk with high accuracy.
In a conventional apparatus for measuring the static friction force between magnetic disk and magnetic head, the magnetic disk is fixed on a mounting base movable by motor having an end thereof secured to a mounting base side fixed end of the apparatus. The magnetic head placed in contact on the magnetic disk, on the other hand, is held by a holder connected to a friction force detector having an end thereof secured to a holder side fixed end of the apparatus.
In the case where the static friction force is measured using a static friction force measuring apparatus configured as described above, a motor is activated to generate an external force and thus to move the mounting base. Then, the maximum output value of the friction detector is detected to calculate the static coefficient of friction is. Specifically, with the head kept in close contact with the magnetic disk under the spring load of the head, the motor is driven at low speed. The maximum output value produced from the friction force detector after starting the motor is determined as a maximum static friction force.
In this conventional static friction force measuring method described above, however, the static friction force between the magnetic disk and the magnetic head cannot be measured accurately, in view of the fact that the true friction force between the magnetic disk and the magnetic head undergoes changes too rapid to be followed by the response characteristic of the friction force detector.
In a method conceived to improve this point, a wide-band sensor high in response speed (about 5 kHz) comprising a combination of a parallel spring and a distortion gage is used as a friction detector. The use of a wide-band sensor as a friction force detector, however, undesirably causes the resonance of the wide-band sensor under the effect of acceleration at the time of starting the motor, thereby making it impossible to determine a true friction force.